The present invention relates to small-diameter or xe2x80x9cslim holexe2x80x9d stage cementers and to related equipment, such as an inflatable packer collar. The slim hole stage cementer of the present invention is designed to facilitate improved drill-out operations.
Stage cementers (xe2x80x9ccementersxe2x80x9d) are used in the petroleum production industry during wellbore-tubular cementing operations. Stage cementers, as that term is used herein, includes (1) stage cementer tools, and (2) stage cementers with inflatable packer collar tools.
Stage cementers intended for use in xe2x80x9cslim-holexe2x80x9d or small diameter casing strings, i.e., casing strings with nominal diameters of 4xc2xdxe2x80x3 inches and smaller, create special problems because of their size. Small diameter cementers inherently present significant problems, both operationally and during drill-out. In relatively larger diameter cementers, many of the problems inherent in the design of the tool may be easily resolved because of the relatively large diameter. Compared to larger diameter cementers, small diameter cementers may present operational challenges not present in the larger tools. As a consequence, stage cementers have conventionally been one type of tool in which the small diameter tools may be more expensive to manufacture because of difficulties inherent in working with reduced diameter components.
Prior art slim-hole stage cementers have been successfully used in the past, but these stage cementers may be very expensive to manufacture, challenging to operate, and difficult to drill out after use. With mechanically-operated stage tools, undrilled portions of a partially drilled out plug may free fall to a lower position within the casing in the wellbore. In addition, drill-out of the moving opening seat may break the seat into several large chunks or pieces. Drilling-up the free floating remnants of an opening seat may be very difficult and risky, with use of the small diameter work strings required to operate inside the small diameter casing. Such small diameter work strings inherently have limited weight on bit and torque capabilities.
A small diameter stage cementer with an inflatable packer collar has, to the knowledge of the applicant, never been manufactured or sold. Stage cementers for nominal casing sizes greater than 4xc2xd inches do not generally present many of the problems associated with small diameter/slim-hole stage cementers.
With the increased cost of drilling, improved wellbore completion technologies, and the need to reduce well drilling costs, slim-hole drilling is becoming increasingly popular. Such popularity has been especially recognized in remote areas. In order to improve realization of the objectives for drilling small diameter wellbores, and to meet the demands for improvements in small-diameter wellbore equipment and procedures, there is a need for an improved stage cementer for use within oilfield casing having a nominal outside diameter 4xc2xd inches or less. Other problems with prior art stage cementers include the difficulty of drilling out the drillable components of the tool after the cementing operation is complete, while still providing a reliably useable and operating tool.
In a larger, more conventionally sized cementer, drill-out of the opening and closing seats may be accomplished relatively easily, in that the internal diameter of the cementer permits use of relatively large drill collars, thereby facilitating applying a relatively substantial weight on bit. If a seat is broken up or free falls, it may be chased by the bit and thereafter effectively drilled up downhole. Such practice is very difficult, relatively expensive, and time consuming in slim-hole casings. Drilling out a slim-hole stage cementer is commonly performed with a slim-hole string, such as 1⅝ inch drill pipe or coiled tubing. Either type of string permits severely limited weight on the bit and limited torque to be transmitted through the drill string to the drill bit.
Other problems are also present in small diameter packer collars configured or manufactured like larger diameter cementers or packer collars. Conventionally sized hydraulically opened stage cementers typically include a cylindrical, sleeve or tubular-shaped outer case surrounding a concentrically positioned, tubular-shaped, inner case, forming a concentric annulus there-between. In a packer collar tool, a port is provided through both cylinders/cases, with the portion of the port through the outer case including a secondary opening device affixed therein, such as a rupture disk, to plug or seal that portion of the port. In operation of the cementer, an opening sleeve is moved to an opened position, exposing the port in the inner case to the interior of the cementer. Thereby, fluid may be pumped from within the casing, through the port in the inner case, through the concentric annulus, and cause inflation of a packer element, positioned on a lower end of the packer collar. The secondary opening device must withstand the inflation fluid pressure without opening until after packer element inflation is complete.
Thereafter fluid pressure is increased causing the secondary opening device to rupture or open, such that the cementing operation may proceed. Cementitious fluid is then pumped through the port in each of the inner and outer cases. Thus, the port in the inner case functions as both a cementing port and an inflation port, and the port in the outer case functions only as a cementing port. The ports may share a common port axis.
Problems arise with small diameter hydraulically operated stage collar cementers and packer collar cementers designed as described above. To effectively and safely place the cement in the wellbore in timely fashion before the cement begins to thicken a minimum fluid pump rate must be obtained through the cementing ports. As a result, the cementing ports in the cementer""s concentric sleeves has a relatively large diameter, as compared to the diameter of a port required to merely inflate the packer. Consequently, in a small diameter tool, the loss of steel or tool material to provide the required port cross-sectional area may limit the tensile working strength of the cementer. This effect may be even more pronounced where the tensile bearing sleeve is the inner sleeve, as this sleeve has an even smaller ID and OD than the outer sleeve, and wall thickness increases are prohibitive to permit a required minimum throughbore ID. The result is a limitation to the amount of casing that can be run below the stage cementer, and/or a limit to the amount of tension that may be pulled in the casing for straightening purposes prior to cementing.
There is thus a need for an improved small diameter stage cementer, a small diameter stage cementer with inflatable packer collar, and a stage cementer, which facilitates improved subsequent drill-out operations. An improved small diameter stage cementer and a method of operating a stage cementer with an inflatable packer collar are subsequently described. The stage cementer and method of this invention thus overcome many of the difficulties and shortcomings of the prior art.
According to a preferred design, both the improved slim-hole stage cementer of the present invention and the combination stage cementer and inflatable packer collar open hydraulically, as do some existing prior art cementers. This hydraulic actuation is a departure, however, from the numerous prior art designs for small diameter, mechanically operated stage cementer tools, which typically require an opening plug to seat on an opening seat to open the ports. Since the present cementer tool is hydraulically opened, this is a significant advantage in tool operation and in cementing, saving time and equipment. A hydraulically operated tool also has the advantage of not requiring drill-out of an opening plug.
Improved drill-out of the cementer according to the present invention is facilitated in one sense, by constructing the drillable portions of the tool, including both the opening and the closing seats, from high strength plastic or composite materials. Improved drill-out is facilitated in another sense, in that when in fully closed positions, both the opening and closing sleeves preferably are splined together and are splined to the lower body to keep components from spinning during the drill-out operation. Drill-out is enhanced in a third and perhaps most significant sense, in that after drilling the first few inches of the opening seat, the bottom portion of the opening seat will fall or be pushed down a few inches to wedge into a reduced ID portion of cementer body. The lower portion of the opening seat may be designed to have a slightly larger OD than the ID of the minimum bore of the lower body. This will cause the lower remaining portion of the opening seat to wedge in the restriction so that the lower portion of the opening seat may be drilled out without rotating or moving under the bit. This interference fit that occurs in the minimum ID of the lower body, where the ID is less than the minimum OD of the opening sleeve substantially assists in drill-out of the opening sleeve.
The opening seat may be fixedly secured to an opening sleeve, such that the two components move between an open and closed position together. The seat portion may be the drillable portion, while the sleeve portion is the permanent portion. In like fashion, the closing seat may be secured to a closing sleeve, wherein the seat is drillable, and the sleeve is permanent.
Hydraulic opening may be facilitated by applying pressure within the casing and cementer throughbore, such that the pressure acts across the differential area between the OD of the seals carried on the opening seat and sleeve, and the corresponding sealing ID on the lower body. The opening pressure may be preset by using selected shear member, such as shear pins or a shear ring. In a disclosed embodiment, the opening seat shear member connects the cementer body to the lower portion of the opening seat. The opening shear mechanism may be located at the lower end of the opening seat in order to facilitate putting the opening pins (or controlled strength shear ring) in pure shear failure (as opposed to a shear-tensile failure), as well as to move the shear location away from areas passed by permanent seals. To change the opening pressure set-point, the cementer may be partially disassembled to change the shear members. In a xe2x80x9cweldedxe2x80x9d version of the tool, the opening pressure may not be adjusted once the tool has been assembled. The closing pressure may be selected and set using a controlled strength shear ring or a shear pin arrangement between the closing sleeve and the body.
For the packer collar version of the tool, inflation of the packer may be facilitated in the same basic fashion as a conventional tool, with a variation for strength considerations. Separate port(s) may be provided for inflation of the packer element, and for conducting cement from inside of the cementer to outside of the cementer.
After the opening sleeve has moved to the opened position, fluid may flow through the small diameter inflation ports and into a concentric/cementer annulus between an inner case/tensile member and an outer case. The inner case/tensile member may be referred to as the cementer mandrel, while the outer case may be referred to as the outer case. The inflation ports may be positioned in a different plane from the cementing ports, such that the inflation ports are located below the cementing ports. The cementing ports may include a rupture disk and equalizer valves positioned within one or more cementing ports in the tensile member of the tool. A stage cementer version of the cementer without the packer would not include an outer case, rupture disk(s), and equalizer valve(s).
Fluid may continue down the cementer annulus between the packer mandrel and the outer case, past a one-way ring check valve and into the packer cavity, inflating and setting the packer. As the packer inflates, pressure is also acting against the rupture disks in the mandrel. When packer has fully inflated and the inflation pressure continues to increase to the predetermined failure pressure of the rupture disk, this disk will rupture, thereby allowing fluid circulation to the wellbore annulus above the inflated packer element and between the outer surface of the casing string and an inner surface of the wellbore. The one-way check valve in the top of the packer element retains the full inflation pressure within the inflated packer element. In a less preferred embodiment, the opening seat on the packer collar could be mechanically set by seating an opening plug thereon.
After the prescribed amount of cement has been pumped, a closing plug may be released and pumped downhole with the tail of the cement, as consistent with known conventional multiple stage cementing practices, to form a pressure shut-off against the closing plug seat. Pressure may be subsequently increased sufficiently to shear the closing sleeve retaining device which holds the closing sleeve in place allowing the closing sleeve to reposition downward to the closed position. When the closing sleeve moves to its fully closed position, a lock-ring located on the OD of the closing sleeve may spring out into an ID undercut near the cementing ports, thereby locking the closing sleeve permanently closed. The undercut in the outer portion of the body also protects the lower set of permanent seals and the closing sleeve from damage while crossing the cementing ports. After the cement has cured sufficiently, the drillable closing and opening seats, and the cement in the cementer may be drilled out. When the top portion of the opening seat is removed during drillout, the lower portion may fall and wedge into the reduced ID restriction in the cementer body, such that the lower portion may be efficiently drilled up without moving under the bit.
It is an object of the present invention to provide an improved slim-hole stage cementer and an improved method of operating a stage cementer.
A feature of the present invention is to provide an improved stage cementer with an inflatable packer collar intended for slim hole (less than or equal to 4xc2xdxe2x80x3 nominal OD) operations.
It is a feature of the present invention that the stage cementer opens hydraulically, rather than being a mechanically opened stage cementer.
Yet another feature of the invention is to provide a stage cementer which facilitates efficient drill-out. A related feature of the invention is that drillable components of both the opening and closing seats may be formed from composite materials. A related feature of the invention is that both the opening and closing seats may be splined together and/or to the lower body to keep components from spinning during the drill-out operation.
Yet another feature of the invention is to provide a stage cementer such that, after drilling the opening seat a short distance, the bottom portion of the drillable opening seat may fall down to a reduced ID in the cementer body. The opening seat may thus wedge in the restriction so that the remaining portion of the seat may be drilled out without undue difficulty.
Yet another feature of the invention is that the tool may be a packer collar version, or a stage cementer version.
Still an additional feature of the invention is that the opening pressure set-point and/or the closing pressure set point may be factory set, or adjusted after initial assembly.
It is a further feature of the invention that the cementer tool may be closed by pumping a closing plug to form a pressure seal against a closing seat. Pressure may then be increased to shear a shearable retaining member which holds the closing sleeve in place. A lock-ring may spring out into the ID undercut in the outer body when the closing sleeve is in the fully closed position, thereby locking the sleeve permanently closed.
It is an advantage of the present invention that the hydraulically inflated packer may be similar to prior art packers, with modifications to packer components. The tool may include cementing ports, rupture disks, and equalizer valves in the mandrel or inner case, and not within the outer case. The packer may be hydraulically set/inflated and the check valve closed to retain the setting pressure in the packer. When the inflation pressure increases to the point of a predetermined failure pressure of the rupture disk(s), the disk(s) will rupture thereby allowing circulation to the wellbore annulus above the inflated packer element.
These and further objects, features, and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings.